Proppant Conveyance System For Fracturing Operations

ABSTRACT

A proppant conveyance system at a well site. The system comprises a sand hopper configured to receive and hold the proppant. The system also includes a prime mover. The system further includes one or more plunger assemblies. Each plunger assembly resides proximate a base of the sand hopper. Each of the plunger assemblies is configured to receive a defined volume of proppant, and transport the defined volume of proppant into a sand manifold in response to power provided by the prime mover. The sand manifold, in turn, is configured to reside in series along a high-pressure frac line. As fracturing fluid moves through the sand manifold, it is mixed with proppant, producing a frac slurry. Methods of forming a frac slurry for use in wellbore fracturing operations are also provided.

STATEMENT OF RELATED APPLICATIONS

This application claims the benefit of U.S. Ser. No. 63/359,329 entitled “Proppant Conveyance System For Fracturing Operations.” That application was filed on Jul. 8, 2022.

This application also claims the benefit of U.S. Ser. No. 63/492,711 filed Mar. 28, 2023. That application was also entitled “Proppant Conveyance System For Fracturing Operations.”

The above applications are incorporated herein in their entireties by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

BACKGROUND OF THE INVENTION

This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is offered to provide a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.

FIELD OF THE INVENTION

The present disclosure relates to the field of hydrocarbon recovery operations. More specifically, the present invention relates to the development of unconventional hydrocarbon resources using proppant. Further still, the invention relates to the injection of a formation fracturing slurry through a wellhead and into a wellbore during a downhole fracturing operation.

Technology in the Field of the Invention

In the completing of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. The drill bit is rotated while force is applied through the drill string and against the rock face of the formation being drilled. After drilling to a predetermined depth, the drill string and bit are removed and the wellbore is lined with a string of casing. The process of drilling and then installing casing is repeated until the wellbore has reached “total depth.”

Advances in drilling technology have enabled oil and gas operators to “kick-off” and steer wellbore trajectories from a generally vertical orientation to a generally horizontal orientation. The horizontal “leg” of each of these wellbores now often exceeds a length of one mile, and sometimes two or even three miles. This significantly multiplies the wellbore exposure to a target hydrocarbon-bearing formation (or “pay zone”). As an example, consider a target pay zone having a (vertical) thickness of 100 feet. A one-mile horizontal leg exposes 52.8 times as much pay zone to a horizontal wellbore as compared to the 100-foot exposure of a conventional vertical wellbore.

Within the United States, many wells are now drilled to recover oil and/or natural gas, and potentially natural gas liquids, from pay zones previously thought to be too impermeable to produce hydrocarbons in economically viable quantities. Such “tight” or “unconventional” formations may comprise sandstone, siltstone, or even shale formations. Alternatively, such unconventional formations may include coalbed methane. In any instance, such formations have “low permeability,” such as less than 0.1 millidarcies.

In order to enhance the recovery of hydrocarbons, particularly in low-permeability formations, stimulation techniques may be employed within the pay zone. Such techniques include hydraulic fracturing and/or acidizing. In addition, “kick-off” wellbores may be formed from a primary wellbore in order to create one or more new directionally or horizontally completed boreholes. This allows the well to penetrate along the depositional plane of more than one subsurface formation to increase exposure to the pay zone. This exposure is further increased by forming multiple fractures along the length of the horizontal wellbore (and any lateral kick-off wellbores), forming so-called “frac-wings.” The frac-wings typically propagate vertically, creating, in essence, multiple vertical completions across the horizontal leg of the single wellbore.

The ability to replicate multiple vertical completions along horizontal wellbores is what has made the pursuit of hydrocarbon reserves from unconventional reservoirs, and particularly shale formations, economically viable within the last fifteen years. This technology has had such an impact that in the United States over 70 percent of all wells are now hydraulically fractured as part of the ordinary well completion process. Further, the total number of frac stages has seen an increase along each horizontal leg as a result of this technology.

A by-product of the industry's success in completing horizontal wellbores in tight formations is a growing need for sand. Those of ordinary skill in the art will understand that sand is mixed into an aqueous fluid used for formation fracturing. The sand serves as a proppant, holding the tight formation open after pumping pressure is released and enabling formation fluids to flow more freely towards the wellbore.

The industry obtains sand from sand mines, most commonly located in Wisconsin, Illinois, Minnesota, and Texas. The sand is transported from the mines to processing plants, either by rail or by barge. In some cases, the sand is filtered on-site (or delivered by a conveyor system to a nearby processing plant) and then delivered to well sites using trucks. Frequently, the sand is stored at the processing site in boxes. From there, the boxes are loaded onto trailers and delivered to individual well sites using trucks.

Sand containers (or boxes) may hold as much as 45,000 pounds of proppant. The boxes are removed from the truck trailers by forklift. During a fracturing operation, sand is first moved from the boxes and onto a conveyor. Some dual conveyor operations are capable of unloading sand at a rate of 50,000 lb/min. The sand is then moved into a blender where it is mixed with water and chemicals, forming a “frac slurry.”

From the blenders, the frac slurry is moved through hoses into frac pumps. The frac slurry passes from a low-pressure cavity to a high-pressure cavity associated with each frac pump. Those of ordinary skill in the art are aware that the blended frac slurry, under pressure, can be highly abrasive. Over time the frac slurry will eat away at the associated piping, packing, plungers, valves, and seats of the frac pumps. This requires frequent maintenance and expense to keep the frac pumps and upstream hose connections operational.

Accordingly, a need exists for a proppant conveyance system wherein the sand is introduced into the fluid medium downstream from the frac pumps. A need further exists for a hydraulic fracturing system wherein the sand is fed into the pipe carrying the fluid medium just before the wellhead, using one or a series of pistons that feed sand at predictable rates.

BRIEF SUMMARY OF THE DISCLOSURE

A proppant conveyance system is first provided herein. The proppant conveyance system is designed to introduce proppant into a fluid medium upstream from the frac tree. In this way, a formation fracturing slurry (or “frac slurry”) is formed. In a preferred arrangement, the only frac iron exposed to the abrasive proppant is the frac tree itself, and possibly a zipper manifold.

The proppant conveyance system first comprises a sand hopper. The sand hopper is preferably a large metal container having an open top. The open top is configured to receive large amounts of proppant at a well site from a truck, a front-end loader, or a forklift.

The proppant conveyance system also includes a prime mover. The prime mover is designed to provide power for moving proppant from the sand hopper into a sand manifold. The prime mover may be, for example, an electric motor or a diesel engine.

The proppant conveyance system also includes one or more pistons. Preferably, five or more pistons are provided. The pistons reside at a base of the sand hopper (or just below the sand hopper). Each of the pistons is configured to receive a defined volume of proppant, and transport that defined volume of proppant into the sand manifold in response to a power input provided by the prime mover. Preferably, proppant is delivered gravitationally to the pistons from the base of the sand hopper; then, the proppant is moved into the sand manifold by the pistons at a rate of 20 to 60 cycles per minute. Preferably, the pistons operate out of phase with each other in order to provide a constant supply of sand to the proppant conveyance system.

The sand manifold is configured to reside in series along a frac line. The frac line receives a blend of water and chemicals from high-pressure pumps. The water and chemicals represent an aqueous carrier medium. As proppant is moved into the sand manifold in cycles, the defined volumes of proppant are mixed with the aqueous carrier medium to form the frac slurry.

In one arrangement, each of the pistons resides within an elongated tubular housing. Each respective tubular housing has a first end configured to receive sand from the sand hopper, and a second end configured to introduce sand into the sand manifold. In one aspect, the elongated tubular housing has an opening along an upper side. The opening is configured to receive the volume of proppant from the base of the sand hopper.

In an arrangement, each of the respective pistons comprises a front body and a rear body. A trough is defined between the front body and the rear body for receiving sand.

In operation, each piston cycles between a retracted and an extended position. In the retracted position, the trough is aligned with the opening along the corresponding elongated tubular housing to receive the volume of proppant. In the extended position, the trough delivers the volume of proppant into the sand manifold. Together, the pistons and their respective tubular housings form plunger assemblies that receive and move sand within the proppant conveyance system.

Preferably, the plunger assemblies also include a rod. The rod has a proximal end which is acted upon by the prime mover, and a distal end which is operatively connected to a rear body of the piston. The rod and connected rear body of the piston are reciprocated by the prime mover.

The sand manifold comprises an inlet end for receiving the aqueous carrier medium upstream of the one or more plunger assemblies, and an outlet end for delivering the frac slurry comprising the aqueous carrier medium and the proppant to the frac tree. Preferably, the proppant comprises sand. The sand is injected into the sand manifold at a rate selected to provide a desired concentration of the sand in the frac slurry.

In one aspect, the front body and the rear body of each piston move together. In this instance, the trough resides between the front body and the rear body of each piston. In another instant, the front body remains stationary within the tubular housing and extends into the sand manifold. A one-way valve resides proximate the second end of the elongated tubular housing. The one-way valve is connected to an end of the front body, and may extend into the sand manifold. As sand is pushed forward by the reciprocating rear body of the piston, the sand moves through the elongated tubular housing, through the front body of the piston, and then through the one-way valve.

A method of forming a hydraulic fracturing slurry is also provided herein. In one aspect, the method includes fluidically connecting a sand manifold to a high-pressure injection line. The sand manifold is placed in series with the high-pressure injection line.

The method also includes receiving a stream of hydraulic fracturing fluid, that is, an aqueous carrier medium, from the high-pressure injection line into the sand manifold. The aqueous carrier medium may comprise a blend of water and chemicals.

Next, the method comprises moving pulses of proppant into the sand manifold such that proppant is mixed with the aqueous carrier medium to form a frac slurry. As a part of this step, a frequency of pulses and a number of piston assemblies may be tuned to inject a desired volume of proppant into the aqueous carrier medium as a function of time.

The method then includes delivering the frac slurry out of the sand manifold and back into the high-pressure injection line. The frac slurry is then moved to a frac tree which is positioned over a wellbore at a well site.

Preferably, the frac slurry is not exposed to frac iron or valves at the well site until it reaches the frac tree or zipper manifold. The only exception might be a so-called fracturing relief valve (“FRV”), which monitors line pressure during a formation fracturing operation. In this method, the amount of corrosion of piping, packing, plungers, valves, and seats of the frac pumps as a result of the abrasive slurry is greatly reduced. Ideally, the proppant is moved into the sand manifold at a constant rate, providing a consistent sand blend in the frac slurry.

A separate method of forming a hydraulic fracturing slurry is also provided herein. In one aspect, the method first comprises providing a sand hopper. The sand hopper is preferably a large metal container having an open top. The open top is configured to receive large amounts of proppant at a well site from a truck, a front-end loader, or a forklift.

The method additionally includes providing a prime mover. The prime mover may be, for example, a hydraulic fluid pump for pumping a clean oil, an electric motor, or an internal combustion engine, such as a diesel engine.

The method also comprises fluidically connecting a sand manifold to a high-pressure injection line. The sand manifold resides in series with the high-pressure injection line.

The method further includes receiving a stream of hydraulic fracturing fluid from the high-pressure injection line into the sand manifold. The sand manifold comprises an inlet end for receiving the fracturing fluid, and an outlet end for delivering the frac slurry comprising the aqueous carrier medium and the proppant.

The method additionally comprises providing one or more plunger assemblies. The plunger assemblies reside along a side of the sand hopper. Each of the plunger assemblies is configured to receive a defined volume of proppant from the sand hopper and transport the defined volume of proppant into the sand manifold in response to motive power provided by the prime mover.

The method also includes conveying sand into the sand hopper. As sand enters the sand hopper, it falls into openings strategically placed along the plunger assemblies. Specifically, the sand falls through openings preserved in elongated tubular housings which house individual pistons. These may be referred to as troughs. Together, the pistons and their respective tubular housings and troughs form the plunger assemblies.

Each respective tubular housing has a first end connected to the sand hopper, and a second end connected to the sand manifold. Each of the respective pistons comprises a front body and a rear body, with the trough being defined between the front body and the rear body.

In operation, each piston cycles between retracted and extended positions. In the retracted position, the trough is aligned with the opening along the corresponding elongated tubular housing to receive the volume of proppant. In the extended position, the trough delivers the volume of proppant into the sand manifold.

The method also includes actuating the pistons in order for each of the pistons to move the defined volume of proppant. Each pulse (or cycle) of the pistons delivers the defined volume of proppant into the aqueous carrier medium while the fracturing fluid moves through the sand manifold. In an arrangement, each of the respective pistons comprises a rod. The rod reciprocates linearly along the elongated tubular housing in response to motive power provided by the prime mover. The reciprocating rod cycles the respective piston between its extended and retracted positions.

The prime mover reciprocates the rod and connected trough at a rate selected to provide a desired concentration of the sand in the slurry. Ideally, the proppant is moved into the sand manifold at a constant rate. Preferably, each piston moves at rate of 20 to 60 cycles per minute. Further, the prime mover may be controlled using a controller. This allows the operator to increase or decrease the rate at which the proppant is moved into the sand manifold to ensure proper blending and concentration. Preferably, the frac slurry is not exposed to frac iron or valves at the well site until it reaches the frac tree or a zipper manifold.

A method of forming a hydraulic fracturing slurry is also provided herein. In one embodiment, the method includes:

-   -   receiving a plurality of sand boxes at a well site;     -   receiving water and chemicals for a wellbore fracturing         operation at the well site;     -   mixing the water and chemicals in selected portions in a blender         to form a liquid frac medium;     -   moving the blended frac medium through one or more high-pressure         pumps;     -   releasing the pressurized and blended frac medium from the one         or more high-pressure pumps and into a high-pressure frac line;     -   pumping the blended frac medium into a sand manifold;     -   transferring sand from the sand boxes into the sand manifold         while pumping the blended frac medium, forming a frac slurry;         and     -   passing the frac slurry from the sand manifold through a frac         tree and into a wellbore.

Ideally, the proppant is moved into the sand manifold at a constant rate. Preferably, the frac slurry is not exposed to frac iron or valves at the well site until it reaches the frac tree or a zipper manifold.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the present disclosures can be better understood, certain illustrations, charts, and/or flow charts are appended hereto. It is to be noted, however, that the drawings illustrate only selected embodiments of the inventions and are therefore not to be considered limiting of scope, for the inventions may admit to other equally effective embodiments and applications.

FIG. 1 is a schematic view of a known well site. The well site is arranged to conduct a hydraulic fracturing operation. A high-pressure injection line is shown transporting formation fracturing fluids across a pressure relief valve en route to a frac tree over a wellbore.

FIG. 2 is a perspective view of an illustrative frac tree. This is an enlarged view of the illustrative frac tree seen in FIG. 1 .

FIG. 3A is a schematic view of a known well site wherein multiple wells are placed (or “zippered”) at a well site. Individual wells are undergoing formation fracturing operations.

FIG. 3B is another schematic view of a well site, similar to that of FIG. 3A. In this view, a sand injection manifold has been placed along the high-pressure injection line.

FIG. 4A is a top view of a proppant conveyance system of the present invention, in one embodiment. The proppant conveyance system includes a sand manifold residing in series with a high-pressure frac line.

FIG. 4B is a front view of the proppant conveyance system of FIG. 4A. Here, the sand manifold has been removed for illustrative purposes.

FIG. 4C is a side view of the proppant conveyance system of FIG. 4A. Here, the sand hopper and the sand manifold are seen.

FIG. 4D is a front plan view of the sand hopper of FIG. 4C. A plunger assembly and the sand manifold have been removed for illustrative purposes.

FIG. 5A is a side, perspective view of a tubular housing. The tubular housing is a part of the plunger assembly for conveying proppant.

FIG. 5B is a side, perspective view of a piston. The piston is configured to cycle in and out of the tubular housing of FIG. 5A. Together, the tubular housing and the piston make up the plunger assembly.

FIG. 6A is a first perspective view of a removable cover used for the tubular housing of FIG. 5A.

FIG. 6B is a second perspective view of the removable cover of FIG. 6A.

FIG. 7A is a first top plan view of the proppant conveyance system of FIG. 4A. Here, a plurality of plunger assemblies are shown residing between the sand hopper and the sand manifold. The sand manifold again resides in series with a high-pressure fracturing fluid line.

FIG. 7B is a second top plan view of the proppant conveyance system of FIG. 4A. It can be seen that the cycling of the pistons of the plunger assemblies are staggered relative to FIG. 7A.

FIG. 8A is a perspective view of the sand manifold of FIG. 4A. A series of inlet flanges is shown. Each inlet flange is configured to receive an end of the tubular housings of FIG. 5A.

FIG. 8B is an enlarged view of one of the inlet flanges of FIG. 8A.

FIG. 8C is a perspective view of a sand manifold in an alternate geometry.

FIG. 9A is a perspective view of a housing for a plunger assembly in an alternate embodiment.

FIG. 9B is an enlarged perspective view of a distal end of the housing of FIG. 9A. Here, a one-way valve residing at a distal end of the piston is more clearly seen.

FIG. 9C is a perspective view of a piston used for a plunger assembly in an alternate embodiment.

FIGS. 10A and 10B together represent a flow chart showing steps for a method of forming a frac slurry.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS Definitions

Various terms as used in the specification and in the claims are defined below. To the extent a term used in the claims is not defined below, it should be given the broadest reasonable interpretation that persons in the upstream oil and gas industry have given that term as reflected in at least one printed publication or issued patent.

For purposes of the present application, it will be understood that the term “hydrocarbon” refers to an organic compound that includes primarily, if not exclusively, the elements hydrogen and carbon. Hydrocarbons may also include other elements such as, but not limited to, halogens, metallic elements, nitrogen, oxygen, and/or sulfur.

As used herein, the term “hydrocarbon fluids” refers to a hydrocarbon or mixtures of hydrocarbons that are gases or liquids. For example, hydrocarbon fluids may include a hydrocarbon or mixtures of hydrocarbons that are gases or liquids at formation conditions, at processing conditions, or at ambient condition. Hydrocarbon fluids may include, for example, oil, natural gas, coalbed methane, shale oil, pyrolysis oil, pyrolysis gas, a pyrolysis product of coal, and other hydrocarbons that are in a gaseous or liquid state, or combination thereof.

As used herein, the terms “produced fluids,” “reservoir fluids” and “production fluids” refer to liquids and/or gases removed from a subsurface formation, including, for example, an organic-rich rock formation. Produced fluids may include both hydrocarbon fluids and non-hydrocarbon fluids. Production fluids may include, but are not limited to, oil, natural gas, pyrolyzed shale oil, synthesis gas, a pyrolysis product of coal, oxygen, carbon dioxide, hydrogen sulfide, and water.

As used herein, the term “fluid” refers to gases, liquids, and combinations of gases and liquids, as well as combinations of gases and solids, combinations of liquids and solids, and combinations of gases, liquids, and solids.

As used herein, the term “subsurface” refers to geologic strata occurring below the earth's surface.

As used herein, the term “formation” refers to any definable subsurface region regardless of size. The formation may contain one or more hydrocarbon-containing layers, one or more non-hydrocarbon containing layers, an overburden, and/or an underburden of any geologic formation. A formation can refer to a single set of related geologic strata of a specific rock type, or to a set of geologic strata of different rock types that contribute to or are encountered in, for example, without limitation, (i) the creation, generation, and/or entrapment of hydrocarbons or minerals, and (ii) the execution of processes used to extract hydrocarbons or minerals from the subsurface.

The term “sand” refers to any granular material containing quartz or silica (meaning a combination of silicon and oxygen, or SiO₂). Non-limiting examples of sand include “Northern White” sand and West Texas eolian sand. Sand is one form of proppant that may be used in a formation fracturing operation.

The term “aggregate” refers to an inorganic mixture containing, at least in part, sand.

As used herein, the term “wellbore” refers to a hole in the subsurface made by drilling or insertion of a conduit into the subsurface. A wellbore may have a substantially circular cross-section. The term “well,” when referring to an opening in the formation, may be used interchangeably with the term “wellbore.”

“Frac,” when used as a prefix or as an adjective, refers to the process known in the art as hydraulic fracturing and denotes that the following word relates to a specific unit, mechanism, or component of the hydraulic fracturing process. Non-limiting examples include “frac pump,” “frac stages,” and “frac slurry.”

“Frac tree” refers to a wellhead that has been specially configured to receive a high-pressure fracturing slurry through one or more valves, and deliver the slurry into the wellbore.

A “well site” is a surface area where one or more wellbores are being or have been formed.

Description of Selected Specific Embodiments

Described herein is a proppant conveyance system used to inject proppant into a high-pressure fracturing fluid line. Also described are methods for forming a frac slurry for injection into a wellbore during a formation fracturing operation.

FIG. 1 is a schematic view of a well site 100 wherein a completion operation is being conducted. More specifically, the well site 100 is undergoing a formation fracturing operation. Fracturing fluids are being injected through a frac tree 200, into a wellbore (shown at 250 in FIG. 2 ) and into a subsurface formation (not shown).

The well site 100 includes a so-called pad 105. The pad 105 represents an area where a surface has been prepared for drilling and completion operations. The pad 105 may be, for example, two to four acres in area. In some cases, more than one well may be drilled and completed on a single pad 105, with each well being completed in the same horizontal plane but in a different azimuth, or optionally, along different horizontal planes.

The well site 100 includes a series of sandboxes 110. The sandboxes 110 represent containers that hold a designated volume of proppant. In FIG. 1 , the sand boxes 110 have been loaded onto trailers of trucks for transport. The sand boxes 110 may be conveniently loaded, unloaded, and stacked using a forklift. An example of such sand boxes 110 are the sand transportation units of SandBox® Logistics located in Houston, Texas.

The well site 100 may optionally include a series of large sand storage trailers 115. The sand storage trailers 115 are carried to the well site 100 using trucks. The sand storage trailers 115 may be pre-filled with sand or may be filled with sand at the well site 100 using a conveyor (not shown). For example, sand may be moved from the sand boxes 110 into the sand storage trailers 115. This allows the smaller sand boxes 110 to be emptied, returned to the sand processing site, and refilled. A completion operation where multiple wells are undergoing formation fracturing at the same well site 100 may utilize several hundred sand boxes 110.

The well site 100 also includes water trucks 120. The water trucks 120 are driven to the well site 100 from typically remote locations. At the well site 100, water may be stored in water tanks 125. The water tanks 125 may represent trailers having water tanks that are pulled to the well site 100 by trucks. This allows the water trucks 120 to unload the water into the water tanks 125 and return to be refilled. In either instance, the water trucks 120 carry water (typically brine) used as the carrier medium for the injection fluid.

FIG. 1 also shows a chemical storage truck 130. The chemical storage truck 130 has been driven onto the pad 105. The chemical storage truck 130 carries surfactants or other chemicals (typically referred to as “slickwater”) that are mixed with the brine contained within the water storage tanks 125 to reduce friction. The surfactants or other chemicals may also optionally include biocides, scale inhibitors, and stabilizers as well as guar gum, which is used as a thickening agent. The surfactants or other chemicals are mixed along with sand into the brine using so-called frac blenders 135. The frac blenders 135 may represent trucks having portable frac blenders that are pulled to the well site 100.

The well site 100 of FIG. 1 also shows a series of frac pumps 150. Each of the frac pumps 150 is preferably part of a truck that is configured to receive injection fluids from the frac blenders 135 to form a slurry. The slurry is then sent under pressure through a high-pressure injection line 175.

A pressure relief valve 178 is typically provided along the high-pressure injection line 175. In the event a pressure is detected along the high-pressure injection line 175 that exceeds a designated threshold pressure, the pressure relief valve (or “frac relief valve” or “FRV”) 178 is opened. Injection fluids are then diverted to an open relief pit 195, where the injection fluids are stored pending future use or disposal.

In recent years, FRV devices have become faster and more sophisticated. An example of such an FRV is found in U.S. Pat. No. 10,550,665 issued to Telos Industries, Inc. in 2020. The teachings of U.S. Pat. No. 10,550,665 relating to pressure control are incorporated herein by reference in their entirety.

In some cases, the frac pumps 150 deliver the slurry to a so-called frac missile 180. (The frac missile is also shown schematically at 370 in FIG. 3A.) Fracturing fluids are delivered to the frac missile 180 via line 165. From there, the fracturing fluids are directed to the frac tree 200 under high pressure, such as 8,000 psig and up to 12,500 psig. In the case of a pad 105 having multiple wells, fluids are directed to a frac manifold (shown schematically at 380 in FIG. 3A), which functions to control a flow of fracturing fluids and direct the flow of fracturing fluids among the respective frac trees 200 throughout the multiple wells at the pad 105.

The well site 100 also includes one or more so-called dog houses 180. The dog houses 180 represent areas where service personnel and operators may work and live during the drilling and completion operations. Not every well site 100 will include dog houses 180; these are simply provided for completeness of disclosure. A service truck 185 may be used to provide tools and equipment such as so-called frac iron, as well as food and supplies for the dog houses 180.

In a hydraulic fracturing (or “fracking”) operation, fluids are pumped into different longitudinal portions of a horizontal wellbore in stages. In addition, a series of different fluids may be pumped into each stage, including, for example, an acid stage, a slickwater stage (having no proppant), a proppant stage and a flushing stage. This application is not intended to be a primer on hydraulic fracturing and the person of ordinary skill in the art will be familiar with the fracking process. For purposes of the present disclosure, all of these fluids, individually and together, are considered “injection fluids,” “fracturing fluids” or a “frac slurry.” In addition, it is understood that FIG. 1 is merely illustrative and that the components shown are not arranged in operational order.

FIG. 2 is a perspective view of the frac tree 200 of FIG. 1 . The frac tree 200 is enlarged for illustrative purposes. The frac tree 200 includes a series of vertically-stacked flow control valves 210. The frac tree 200 also includes a series of horizontally-oriented flow control valves 220. The flow control valves 210, 220 control the high-pressure injection of fracturing fluids into the wellbore 250.

A pressure gauge 230 resides on the frac tree 200. It is understood that the pressure gauge 230 will likely be a digital sensor that is in wireless electrical communication with a controller (not shown). During normal operation of the well site 100 and the frac tree 200, injection fluids pass through the high-pressure injection line 175 into the frac tree 200 and into the wellbore 250. In the event pressure in the frac tree 200 exceeds a designated threshold pressure, the controller will send a signal to the FRV 178 to open, diverting fluids into the open relief pit 195. Similarly, if a pressure is detected along the high-pressure injection line 175 that exceeds the designated threshold pressure, then a series of plug valves of the FRV 178 are opened and injection fluids are released to the open relief pit 195.

It is understood that the current disclosures are not limited by the architecture of the frac tree 200 or the operation of any specific FRV 178.

FIG. 3A is a schematic view of a known well site 300A wherein multiple wells 390 are placed (or “zippered”) at the well site 300A. The individual wells 390 are undergoing formation fracturing operations, meaning that fracturing fluid is being injected into the wellbores (shown at 250 in FIG. 2 ) and formations associated with the respective wells 390.

Those of ordinary skill in the art will understand that in some cases multiple wells 390 will be fractured together, in stages, in order to take advantage of the same sand boxes 110, the same water trucks 120, and other equipment on the well pad 105. Illustrative well site 300A does not include all of the components of the formation fracturing operation; instead, illustrative well site 300A only shows selected components schematically for the injection of a frac slurry into the wells 390.

In FIG. 3A, a plurality of sand boxes 310 are shown. The sand boxes 310 contain proppant to be used as part of the frac slurry. These may be in accordance with sand boxes 110 described above.

The well site 300A also includes a plurality of water tanks 320. These may be in accordance with the water trucks 120 described above or may comprise of free-standing tanks. In addition, the well site 300A includes chemical tanks 330. Again, these may be in accordance with the chemical storage trucks 130 described above or may comprise of free-standing tanks. Proppant, water, and chemicals are moved from their respective tanks 310, 320, 330 into frac blenders 350, where they are mixed in desired proportions to form the frac slurry. The frac slurry moves through lines 355 and into high-pressure pumps 360. While six high-pressure pumps 360 are shown in illustrative well site 300A, it is understood that in some operations only one or two pumps 360 may be required.

The high-pressure pumps 360 typically reside on trucks, which may be referred to as pumping trucks. It is understood that the pumping trucks are capable of being moved about the well site 300A and contain necessary equipment, to include at least one prime mover, to facilitate the formation fracturing operation. The pressurized frac slurry leaves the pumping trucks 360 and travels through jumper lines 365 to the frac missile 370. The frac missile 370 comprises a collection of valves used to control the movement and flow rate of the frac slurry into a high-pressure injection line 375. The frac slurry will move across a pressure relief valve (or “frac relief valve,” or “FRV”) 378. The frac slurry is then delivered to the frac tree (shown at 200 in FIG. 2 ) over the respective wells 390.

In some cases, frac slurry is injected into more than one well 390 at a time. In this instance, a separate frac manifold 380 may optionally be used. The frac manifold 380 will include appropriate valves for controlling the flow of frac fluids to selected wells 390. Of course, where only one well 390 is present, the frac manifold 380 and separate injection lines 385 are not needed.

Current completion operations operate under the principle that “more sand is better.” It is estimated that a standard horizontal well now uses between 1,900 pounds (nearly 1 ton) and 3,000 pounds (1.5 tons) of sand per lateral foot. A 10,000 foot lateral well may consume 12 million to 25 million pounds (6,000-12,500 tons) of proppant, which is mixed into a water-based slurry using mixers and blenders. While only a few illustrative sand boxes 310, water tanks 320, and chemical tanks 330 are shown at well site 300A, it is understood that the fracturing operation for a 10,000 foot lateral well may require a delivery of sand and water by over 450 trucks. A single frac crew can place downhole 4 million pounds or more of sand in a day, emptying, for example, 100 dry bulk trailers every 24 hours.

The delivery of the frac slurry and its large volumes of sand is accomplished at high-pressures and pump rates. Those of ordinary skill in the art will understand that the movement of frac slurry through lines 355, through the pumping trucks 360, through jumper lines 365, through the frac missile 370, through the high-pressure injection line 375, and all of the valves and connections, is a highly abrasive operation. The abrasive nature of the frac slurry may result in a breakdown of components, resulting in a need for maintenance and may cause delay in operation and potentially cessation of fracturing operations.

In one arrangement, lubricant may be injected into the flow control valves 210, 220 associated with the frac tree 200 during the fracturing operation. The lubricant is placed under pressure prior to releasing frac fluids through the frac tree 200 and into the wellbore 390. This is done to protect the valves and valve seats of the frac tree 200 from the abrasive nature and erosive effects of high-pressure fluid injection. Such a procedure is described in U.S. Pat. No. 10,358,891 issued to Christopher Knott in 2019. However, the remaining frac iron not contained within the frac tree 200 remains exposed to sand.

FIG. 3B is another schematic view of a well site 300B. The well site 300B is similar to the illustrative well site 300A of FIG. 3A. Well site 300B also includes the sand boxes 310, the water tanks 320, the chemical tanks 330, the pumping trucks 360, the jumper lines 365, and the frac missile 370. However, in this arrangement the sand boxes 310 have been moved downstream of the frac missile 370. In this way, all of the connections and frac iron from the blenders 350 down to the frac missile 370 are spared exposure to the abrasive proppant.

Irrespective of an arrangement of components at the well site 300B, it remains necessary to introduce proppant into the frac slurry. To this end, one or more sand hoppers 340 are employed. The sand hoppers 340 are configured to receive sand from the sand boxes 310, such as through a conveyor belt 315. The sand is moved from the sand hoppers 340 into the high-pressure injection line (or “frac line”) 375 in real time during the frac operation.

To facilitate the introduction of sand into the frac line 375, a sand manifold 470 may be placed in line with the frac line 375. The sand manifold 470 is a pressure vessel specially configured to receive frac fluid from the frac line 375 at an inlet end, while also receiving volumes of dry sand, such as from the sand hoppers 340. The sand manifold 470 then expels the mixture as a frac slurry, which may comprise frac fluid and sand, that moves on to the frac manifold 380 (or, as the case may be, a frac tree 200).

To move dry sand into the sand manifold 470, specially-designed plunger assemblies 440 are provided. The plunger assemblies 440 receive sand from the sand hopper 340 and deliver the sand in separate volumes to the sand manifold 470. Together, the sand hopper 340, the plunger assemblies 440, and the sand manifold 470 form a proppant conveyor system.

FIG. 4A is a top view of a proppant conveyance system 400 of the present invention, in one embodiment. The proppant conveyance system 400 comprises the sand hopper 340. The sand hopper 340 has an open top 410. Slanted base walls 412 gravitationally direct sand through the open top 410 and down to the individual plunger assemblies 440.

Each plunger assembly 440 comprises an elongated tubular housing 445. Each tubular housing 445 includes an opening 447 that gravitationally receives proppant from above. In addition, each plunger assembly 440 includes a piston (seen at 450 in FIG. 5B). Each piston 450 generally resides within its respective tubular housing 445 but is configured to cyclically and slidably move between a retracted position and an extended position.

Each tubular housing 445 has a distal end (shown at 444 in FIG. 5A). The distal end 444 connects to a side 475 of the sand manifold 470 by means of a flange 430. Each piston 450 also has a distal end (shown at 454 in FIG. 5B). In the arrangement of FIG. 4A, the distal end 454 of each piston 450 comprises a dart 472. Preferably, the darts 472 are fabricated from an elastomeric material such as a synthetic rubber.

In the view of FIG. 4A, five pistons 450 are shown. Each piston 450 is shown in its retracted position. It can be seen that the darts 472 have been withdrawn back to the flanges 430 along the side wall 475 of the sand manifold 470. In operation, the darts 472 aid in mixing the slurry S during the extension portion of the cycle of the piston 450. The darts 472 then function as a check valve during the retraction portion of the cycle of the piston 450, maintaining pressure in the high-pressure sand manifold 470 when sealed in place.

Of interest, each piston 450 moves along a guide rod 474. Optionally, the guide rods 474 traverse an inner diameter of the sand manifold 470. The guide rods 474 support the pistons 450 and connected darts 472 as they are extended into the sand manifold 470 and then retract back into their respective tubular housings 445.

As noted, the sand manifold 470 resides in series along the high-pressure injection line 375. The sand manifold 470 has an inlet end 471 and an outlet end 473. In one aspect, each of the inlet end 471 and an outlet end 473 may be a 7″ full bore pipe.

An aqueous fluid W is received at the inlet end 471. The aqueous fluid W is comprised of water (typically brine) and fracturing chemicals. The flow of the aqueous fluid W is shown using an arrow. The aqueous fluid W mixes with proppant that is injected into the sand manifold 470 via the sand hopper 340 and respective components. This forms a frac slurry S. The frac slurry S leaves the sand manifold 470 at the outlet end 473, indicated also by means of an arrow, via the high-pressure line 375.

FIG. 4B is a front view of a portion of the proppant conveyance system 400 of FIG. 4A. Here, the sand manifold 470 has been removed from the proppant conveyance system 400 for illustrative purposes. Similarly, the plunger assemblies 440 are removed. Essentially, only the sand hopper 340 and flanges 430 are seen.

It can be seen that the sand hopper 340 has side walls 411. The side walls 411 form a substantially rectangular shape and contain sand that is dropped into the open top 410 by the conveyor 315 or, optionally, using equipment such as a frontend loader. Proppant moves gravitationally down the sand hopper 340 and is guided by the slanted base walls 412. The proppant is then received within the openings 447 along the tubular housings (shown at 445 in FIG. 4A).

The sand hopper 340 is supported by one or more legs 414. Ideally, each leg 414 is only one to three feet off of the ground, enabling sand to be pumped into the sand manifold 470 without having to adjust a height of the frac injection line 375.

FIG. 4C is a side view of the proppant conveyance system 400 of FIG. 4A. Here, the sand hopper 340 is again shown. The dart 472 is again seen in its retracted position against the side wall (shown at 475 in FIG. 4A) of the sand manifold 470.

Of interest in FIG. 4C, a prime mover 480 is shown. The prime mover 480 is used to the reciprocate the pistons 450 within the respective housings 445. Preferably, the prime mover 480 is an electric motor with an electric drive. In an alternate embodiment, the prime mover 480 may comprise a diesel engine with an electric drive. Cycling of the pistons 450 injects sand into the sand manifold 470 at a desired rate.

In the arrangement of FIG. 4C, the prime mover 480 is supported by legs 481. The legs 481 elevate the prime mover 480 so that one or more drive lines 484 is in line with the plunger assemblies 440. Specifically, the drive lines 484 are in-line with the rods 455 of the pistons 450.

FIG. 4D is a front plan view of the sand hopper 340 of FIG. 4C. The plunger assembly 440 and sand manifold 470 have been removed for illustrative purposes. In this view, a plurality of openings 345 are provided along a bottom end of the slanted base walls 412. These openings 345 are dimensioned to closely receive respective tubular housings 445.

Granular proppant 240 is seen within the sand hopper 340. The proppant 240 has fallen through recesses 415 provided above each opening 345. The recesses 415 are configured to gravitationally release the proppant 240 into the respective openings (shown at 447 of FIG. 5A) of the tubular housings 445.

FIG. 5A is a side, perspective view of the tubular housing 445 from FIG. 4A. The tubular housing 445 has a first (or proximal) end 442 and the second (or distal) end 444. The proximal end 442 extends into a base (shown at 420 in FIG. 4B) of the sand hopper 340, while the distal end 444 is secured to the flange 430. End flange 443 is configured to receive bolts (not shown) that connect to the flange 430. In this way, the tubular housing 445 is capable of being secured to the sand manifold 470, however, the tubular housing 445 remains removably attachable to the sand manifold 470 in the event of maintenance or replacement.

The tubular housing 445 defines a generally cylindrical body 441. An inner bore 433 is formed within the cylindrical body 441. The cylindrical body 441 is interrupted by the opening 447. The opening 447 is configured to receive proppant from the sand hopper 340. Proppant is indicated schematically by Arrow P entering from above at the opening 447.

Optionally, a pair of dovetails 449 extend from the cylindrical body 441. The pair of dovetails 449 mate into corresponding openings along the sand hopper 470. These allow for removable connectivity between the cylindrical body 441 and the sand hopper 470 and also prevent the tubular housings 445 from rotating during operation of the pistons 450.

As noted, the tubular housing 445 is a part of the plunger assembly 440 used for conveying proppant. To convey proppant, the piston 450 is provided within the tubular housing 445. Together, the tubular housing 445 and the piston 450 make up the plunger assembly 440.

FIG. 5B is a side, perspective view of the piston 450, in one embodiment. The piston 450 is configured to reside within and cycle in and out of the tubular housing 445 of FIG. 5A. The piston 450 has a first end 452 and the second (or distal) end 454. The first end 452 resides within the base 420 of the sand hopper 340. The first end 452 slidably houses a rod 455. The rod 455 reciprocates back and forth in response to motive power provided by the prime mover (shown at 480 in FIG. 4C).

The second end 454 slides in and out of the tubular housing 445. The dart 472 is connected to the second end 454 but always resides within the sand manifold 470.

The piston 450 includes a stationary block 453. A through-opening is preserved along the stationary block 453 that slidably receives the rod 455. Thus, as the rod 455 moves back and forth within the tubular housing 445, the stationary block 453 remains in a fixed position within the tubular housing 445.

The piston 450 also includes a front body 456 and a rear body 458. The front 456 and rear 458 bodies are connected to the rod 455. As the rod 455 moves back and forth within the tubular housing 445, the front 456 and rear 458 bodies also move. Beneficially, the stationary block 453 also serves as a stop that keeps the rear body 458 from traveling too far backwards during its stroke.

A gap 457 is preserved between the front 456 and rear 458 bodies. The gap 457 may be referred to as a trough. When the piston 450 is in its retracted position, the trough 457 is aligned with the opening 447. This allows the trough 457 to receive a volume of proppant. In its extended position, the opening 447 is closed by the piston 450, and the trough 457 delivers the volume of proppant into the sand manifold 470.

Optionally, a pair of scrapers 451′, 451″ is placed along the piston 450. Scraper 451″ resides around the front body 456, while scraper 451′ resides around the rear body 458. The pair of scrapers 451′, 451″ assist in removing proppant delivered through the opening 447 from a wall of the inner bore 433 within the cylindrical body 441 and also provide a fluid seal for the trough 457 when the pistons 450 of the plunger assemblies 440 move between the retracted and extended positions. Each of the pair of scrapers 451′, 451″ may include O-rings to aid in providing the fluid seal.

FIG. 6A is a first perspective view of a removable cover 460 used for the plunger assemblies 440 of FIG. 5A. FIG. 6B is a second perspective view of the removable cover 460 of FIG. 6A. The removable cover 460 may be described with reference to FIGS. 6A and 6B together.

The cover 460 has a first end 462, and a second end 464 opposite the first end 462. The cover 460 defines an arcuate body 465 having an outer surface 466 and an inner surface 469. The cover 460 is configured to reside inside of the tubular housing 445. More specifically, the cover 460 covers an opening where the proppant might otherwise fall. The cover 460 follows the piston 450 to reciprocate back and forth during its cycle and keeps sand from entering the piston 450 during an extension phase of the cycle.

FIG. 7A is a first top plan view of the proppant conveyance system 400 of FIG. 4A. Here, the plurality of plunger assemblies 440 are shown residing between the sand hopper 340 (see via base 420) and a sand manifold 470. The sand manifold 470 again resides in series with a high-pressure fracturing fluid line 375. It can be seen that the cycling of the pistons 450 of the plunger assemblies 440 is staggered. This is an option that helps keep a rate of proppant injected into the sand manifold 470 at a substantially constant rate. Optionally, the cycling of the pistons 450 of the plunger assemblies 440 may be altered to manipulate the rate of proppant P injected into the sand manifold 470, thus allowing for the rate to be increased or decreased as needed.

FIG. 7B is a second top plan view of the proppant conveyance system 400 of FIG. 4A. It can be seen that the cycling of the pistons 450 of the plunger assemblies 440 are now staggered relative to FIG. 7A. The guide rods 474 are seen supporting the front 458 and rear 456 bodies. It is understood that this is one illustrative embodiment. In other arrangements (such as that shown in FIGS. 9A and 9B discussed below), no guide rod 474 is used and the moving body 955 does not extend into the sand manifold 470.

FIG. 8A is a perspective view of the sand manifold 470 of FIG. 4A. A series of inlet flanges 430 is shown. Each inlet flange 430 is configured to receive an end of the tubular housings 445 of FIG. 5A. In addition, each inlet flange 430 receives a stationary guide rod 474. Each inlet flange 430 is configured to receive bolts (not shown) which allows the tubular housing 445 to be removably attachable to the sand manifold 470.

FIG. 8B is an enlarged view of one of the inlet flanges 430 of FIG. 8A. Here, bolt holes are more clearly seen.

FIG. 8C is a perspective view of a sand manifold 870 in an alternate geometry. It can be seen that the sand manifold 870 has an inlet end 872 and an outlet end 874. The sand manifold 870 is designed to be placed in-line with the high-pressure frac line 375. Thus, the high-pressure frac line 375 is connected to the sand manifold 870 at each of the inlet 872 and outlet 874 ends.

A flange 875 is placed at the inlet end 872. The flange 875 provides a removable connection to the high-pressure frac line 375. It is understood that an identical flange 875 is placed at the outlet end 874 of the sand manifold 870 to removably connect with the high-pressure frac line 375.

The sand manifold 870 also includes a top wall 876 and a side wall 878. The sand manifold 870 may be supported above a ground surface by legs 814.

Along the side wall 878 is a series of side flanges 430. Each side flange 430 is connected to an elongated tubular housing 445. In the view of FIG. 8C, only a short portion of each tubular housing 445 is shown.

FIG. 9A is a perspective view of a housing 945 for a plunger assembly in an alternative embodiment. As with housing 445 of FIG. 5A, the housing 945 defines a cylindrical body 941 having a first end 942 and a second end 944. The first end 942 extends into the base 420 of the sand hopper 340. The first end 942 also slidably houses a rod 955. The second end 944 comprises an end flange 943. The end flange 943 is configured to be secured to the flange 430 of the sand manifold 470 using bolts (not shown). In this way, the housing 945 is secured to the sand manifold 470.

A bore 933 is formed within the cylindrical body 941. The cylindrical body 941 is interrupted by an opening 947. The opening 947 is configured to receive proppant from the sand hopper 340. Proppant is again indicated schematically by Arrow P entering from above at the opening 947. In one aspect, the opening 947 is one foot in length.

As noted, the tubular housing 945 is a part of a plunger assembly used for conveying proppant. To convey proppant, a piston (shown at 950 in FIG. 9C) is provided within the tubular housing 945. Together, the tubular housing 945 and the piston 950 make up the plunger assembly in an alternate arrangement.

FIG. 9B is an enlarged perspective view of the distal end 944 of the housing 945 of FIG. 9A. Here, a one-way valve 960 can be seen extending from the distal end 944 of the housing 945. The one-way valve 960 represents a so-called flapper valve. The flapper valve 960 comprises a body 961. The body 961 may be threadedly attached to the second (or distal) end 944 of the housing 945. More preferably, the body 961 is threadedly connected to and extends out from the piston 950. Such an arrangement is shown in FIG. 9C.

The one-way valve 960 comprises a flapper 965. The flapper 965 is pivotally connected to the body 961 by means of a pivot member 967. Typically, the pivot member 967 will include a spring (not shown) that biases the flapper 965 in a closed position. In FIG. 9A, the flapper 965 is in its open position, while in FIG. 9B the flapper 965 is in its closed position. An elastomeric sealing member 963 resides between the flapper 965 and the body 961 when the flapper 965 is in its closed position.

FIG. 9C is a perspective view of the piston 950 used for a plunger assembly with the tubular housing 945 of FIG. 9A. It can be seen that as with the piston 450 of FIG. 5B, the piston 950 is comprised of two parts—a front body 980 and a rear body 955. In piston 450, the front 456 and rear 458 bodies are connected by the rod 455. Thus, as the rod 455 cycles back and forth within the tubular housing 445, the front 456 and rear 458 bodies also move together. However, in piston 950 only the rear body 955 is connected to and acted upon by the rod 945. This means that the front body 980 remains stationary within the housing 945 as the piston 950 cycles from its retracted position to its extended position

In FIG. 9C, Arrows S are shown to indicate a stroke of the rod 945 and connected rear body 955. The rod 945 and rear body 955 cycle back and forth within the housing 945 in response to power provided by a prime mover (not shown). In FIG. 9A, dimension L indicates a length of the stroke S, in one arrangement.

Of interest, FIG. 9A shows a first (or proximal) end 982 of the front body 980 in phantom. FIG. 9A also shows the rear body 955 in phantom. Note that the rear body 950 is in its retracted position within the housing 945. This leaves the opening 947 in the housing 945 clear to receive sand from the sand hopper 340. When the rear body 955 strokes forward, sand (or other proppant) will be pushed forward towards the distal end 944 of the housing 945. As the rear body 955 continues to cycle according to its stroke length L, sand will be pushed out of the housing 945 and through the one-way valve 960. From there, sand enters the sand manifold 470.

Optionally, a stop ring (shown at 949 in FIG. 9A) is placed along an inner diameter of the housing 945 downstream from the opening 947. The stop ring 949 keeps the rear body 955 from advancing too far into the housing 945 during its forward stroke S.

Returning to FIG. 9C, the rear (or cycling) body 955 of the piston 950 defines a cylindrical body 951. In this respect, the cylindrical body 951 is preferably hollow, creating the inner bore 933. The cylindrical body has a first (or proximal) end 952 and a second (or distal) end 954. In one aspect, the second end 954 is filed down to have a thin diameter at a leading edge 957. This reduces friction as the rear body 955 pushes sand towards the flapper valve 960 during cycling.

Optionally, an annular ring 959 is provided around the cylindrical body 951 of the rear body 955. The annular ring 959 resides proximate the second end 954 of the cylindrical body 951. The annular ring 959 is preferably fabricated from a highly durable plastic and keeps sand from lodging in the annular area between the rear body 955 and the surrounding housing 945. The annular ring 959 essentially serves as a scraper.

At the first end 952 of the rear body 955 is a push plate 956. The push plate 956 connects the rod 945 to the rear body 955. The push plate 956 also seals the first end 952 of the rear body 955, allowing the rear body 955 to move sand forward on each stroke S.

As noted, the piston 950 also includes a front (or stationary) body 980. The stationary body 980 also includes a first (or proximal) end 982 and a second (or distal) end 984. The body 961 of the one-way valve 960 may be threadedly or adhesively connected to the distal end 984 of the stationary body 980. The stationary body 980 of the piston 950 defines a cylindrical member 981. The cylindrical member 981 and the valve body 961 are both hollow, allowing sand to be pushed through them in pulses.

Two seal rings 983, 987 are placed along the cylindrical member 981 of the stationary body 980. Seal ring 983 resides upstream from the end flange (shown at 943 in FIG. 9A), while seal ring 987 resides downstream from the end flange 943. In one aspect, seal ring 987 actually resides within the sand manifold 470. In any event, the seal rings 983, 987 prevent sand from backing out of the sand manifold 470 in response to its high pressure environment.

It is observed that the front (or stationary) body 980 is optional. As noted in connection with FIGS. 9A and 9B, it is possible to attach the one-way valve 960 to the distal end 944 of the housing 945 itself. This places the one-way valve 960 within an interior of the sand manifold 470. However, it is preferred to attach the one-way valve 960 to the stationary body 980. This allows the operator to adjust a position of the stationary body 980 (and its attached one-way valve 960) relative to the housing 945, which in turn adjusts the location of the one-way valve 960 within the sand manifold 470. Those of ordinary skill in the art will understand that it is desirable to inject the pulses of proppant into a center (or at least close to a center) of the sand manifold 470 during operation. This helps provide consistent blending of proppant into the frac slurry.

It is further observed that in the arrangement of FIGS. 9A-9C, the operator need not employ the guide rods 474 of FIGS. 7A and 7B. While the plunger assembly arrangement of FIGS. 9A-9C does not provide for the extent of mixing of the slurry as with the plunger assembly of FIGS. 7A-7B, the plunger assembly of FIGS. 9A-9C does allow the operator to simply push the proppant through the one-way valve 960. To enhance mixing, the operator may then optionally place one or more internals (e.g., plates or baffles) within the sand manifold 470 to interrupt the flow of frac slurry before it exits the sand manifold 470.

Based on the proppant conveyance system 400 described above and the sand manifolds 470, 870, a method of forming a frac slurry is provided herein. FIGS. 10A and 10B together provide a flow chart showing steps for a method 1000 of forming a frac slurry, in one embodiment.

The method 1000 first comprises receiving a plurality of sand boxes at a well site. This is shown in Box 1010. The sand boxes contain proppant to be mixed into an aqueous medium.

The method 1000 next includes receiving water and chemicals for a wellbore fracturing operation at the well site. This is seen at Box 1020. The water and chemicals are also delivered to the well site.

The method 1000 further comprises mixing the water and chemicals in selected portions in a blender. This is indicated at Box 1030. The water and chemicals are mixed to form an aqueous carrier medium, also known as a liquid frac medium.

The method 1000 additionally includes moving the blended aqueous carrier medium through one or more high-pressure pumps. This is shown in box 1040. In one aspect, the fluid is pressurized in excess of 8,000 psig.

The method 1000 also comprises delivering the pressurized aqueous carrier medium from the high-pressure pumps into a high-pressure frac line. This is indicated at Box 1050 of FIG. 10A.

Next, the method 1000 includes pumping the blended aqueous carrier medium through a sand manifold. This is provided at Box 1060. The sand manifold is a high-pressure vessel residing in series with the high-pressure frac line.

Also, the method 1000 comprises transferring sand from the sand boxes and into the sand manifold. This is seen at Box 1070. In a preferred embodiment, the proppant comprises sand. The transfer of sand into the sand manifold is done while pumping the blended aqueous carrier medium through the high-pressure frac line. This forms a frac slurry.

In a preferred arrangement, the proppant is moved into the sand manifold at a constant rate. This is shown in Box 1080. Injecting proppant at a constant rate may be done by the injection of sand into the sand manifold using pistons, wherein the pistons move in a staggered manner. Each piston injects a defined volume of dry sand with each cycle, the defined volume being a product of a bore and a stroke of each piston. The pistons may operate at a rate of, for example, 20 Hertz, injecting 10,000 pounds of sand per hour, each. The pistons are driven by a prime mover. The prime mover may include, for example, an electric motor, a diesel engine, or a hydraulic pump.

In one aspect, the rate of movement of the pistons is controlled by means of a controller. In addition, the movement of the pistons may be staggered using the controller. The controller may be set or adjusted remotely to keep personnel out of the so-called red zone.

The method 1000 additionally includes passing the frac slurry through a frac tree and into the wellbore. This is provided at Box 1090. Preferably, the frac slurry is exposed to no frac iron at the well site until it reaches the wellhead where the frac tree is located. The only possible exception might be a frac manifold (such as manifold 380 of FIG. 3B) or an FRV (such as FRV 378 of FIG. 3B).

As can be seen, an improved method for forming a formation fracturing slurry is provided. Further variations of the proppant conveyance system and the methods of transporting proppant for wellbore operations herein may fall within the spirit of the claims, below. For example, the plunger assemblies 440 may include pressure equalization lines. The lines direct air from the sand manifold 470 back to the individual pistons 450 as the pistons 450 move in and out during their stroke. In this way, air is not introduced into the frac system.

It will be appreciated that the present disclosure and inventions are susceptible to modification, variation and change without departing from the spirit thereof. 

I claim:
 1. A proppant conveyance system, comprising: a sand hopper configured to receive proppant; a prime mover; a sand manifold; and one or more pistons residing at a base of the sand hopper, with each of the one or more pistons being configured to receive a defined volume of proppant from the sand hopper, and transport the defined volume of proppant into the sand manifold in response to power provided by the prime mover; and wherein the sand manifold is configured to reside in series along a high-pressure frac line.
 2. The proppant conveyance system of claim 1, wherein: the prime mover comprises a hydraulic fluid pump for pumping a clean oil, an electric motor, or an internal combustion engine.
 3. The proppant conveyance system of claim 1, wherein: the one or more pistons comprises two or more pistons; each of the pistons resides within an elongated tubular housing, wherein each respective elongated tubular housing has a first end connected to the sand hopper, and a second end connected to the sand manifold; and together, the pistons and respective elongated tubular housings form plunger assemblies.
 4. The proppant conveyance system of claim 3, wherein: the elongated tubular housing further comprises an opening along an upper side configured to receive the volume of proppant; and each of the one or more respective pistons comprises a front body and a rear body, with a trough residing between the front body and the rear body, and wherein each piston cycles between a retracted position and an extended position such that: when the piston is in its retracted position, the trough is aligned with the opening along the corresponding elongated tubular housing to receive the volume of proppant, and when the piston is in its extended position, the trough delivers the volume of proppant into the sand manifold.
 5. The proppant conveyance system of claim 4, further comprising: a manifold that sealingly secures each elongated tubular housing for the respective plunger assemblies to the sand manifold; and wherein the sand manifold comprises an inlet end for receiving a fracturing fluid upstream of the plunger assemblies, and an outlet end for delivering a frac slurry comprising the fracturing fluid and the proppant.
 6. The proppant conveyance system of claim 5, wherein the proppant comprises sand.
 7. The proppant conveyance system of claim 5, wherein each of the one or more respective pistons further comprises: a rod that reciprocates linearly along the elongated tubular housing in response to motive power provided by the prime mover; a first end residing at the sand hopper that slidingly receives the rod; a stationary plate residing proximate the first end, with the stationary plate having an opening for receiving the rod and serving as a stop member for the rear body when the plunger moves to its retracted position; and a second end residing at a distal end of the front body.
 8. The proppant conveyance system of claim 5, wherein each of the one or more respective pistons further comprises: an elastomeric dart residing at the distal end of the front body but within the sand manifold, serving as a seal to the elongated tubular housing when the plunger moves to its retracted position; a first O-ring residing around an outer diameter of the front body; and a second O-ring residing around an outer diameter of the rear body; wherein the first O-ring and the second O-ring provide a fluid seal for the trough when the plunger moves to its retracted position.
 9. The proppant conveyance system of claim 5, wherein each of the one or more respective pistons further comprises: a rod that reciprocates linearly along the elongated tubular housing in response to motive power provided by the prime mover; and a push plate connecting the rod to the first end of the rear body; and wherein: the rear body is connected to the rod, such that the rear body cycles within the elongated tubular housing between retracted and extended positions in response to reciprocation of the rod; and in its retracted position the rear body resides between the base of the sand hopper and the opening along the upper side of the elongated tubular housing.
 10. The proppant conveyance system of claim 9, further comprising: a one-way valve residing proximate the second end of the elongated tubular housing, wherein the one-way valve extends into the sand manifold.
 11. The proppant conveyance system of claim 10, wherein: the front body of each of the one or more respective pistons is stationary, and resides at the distal end of its respective elongated tubular housing; and the one-way valve resides at the distal of and is connected to the front body of each of the one or more respective pistons.
 12. The proppant conveyance system of claim 11, wherein the prime mover reciprocates the rods at a frequency selected to provide a desired concentration of the proppant into the frac slurry.
 13. The proppant conveyance system of claim 11, wherein the prime mover reciprocates the rods in a staggered manner such that the injection of the volumes of proppant into the sand manifold is at a generally constant rate.
 14. A method of forming a hydraulic fracturing slurry, comprising: fluidically connecting a sand manifold to a high-pressure injection line, in series with the high-pressure injection line; receiving a stream of hydraulic fracturing fluid from the high-pressure injection line into the sand manifold; moving pulses of proppant into the sand manifold such that proppant is mixed with the hydraulic fracturing fluid to form a frac slurry; delivering the frac slurry out of the sand manifold and back into the high-pressure injection line; and moving the frac slurry to a frac tree positioned over a wellbore at a well site.
 15. The method of claim 14, wherein: the frac slurry is exposed to no frac iron at the well site other than a pressure relief valve until it reaches the frac tree; and the proppant is moved into the sand manifold at a generally constant rate.
 16. A method of forming a hydraulic fracturing slurry, comprising: providing a sand hopper; providing a prime mover; fluidically connecting a sand manifold to a high-pressure injection line, in series with the high-pressure injection line; receiving a stream of hydraulic fracturing fluid from the high-pressure injection line into the sand manifold; providing one or more plunger assemblies residing at a base of the sand hopper, with each of the one or more plunger assemblies being configured to receive a defined volume of proppant, and transport the defined volume of proppant into the sand manifold in response to motive power provided by the prime mover; conveying proppant into the sand hopper; and actuating the one or more plunger assemblies in order to move the defined volume of proppant from each of the one or more plunger assemblies as pulses while the hydraulic fracturing fluid moves through the sand manifold.
 17. The method of claim 16, wherein: the prime mover comprises a hydraulic fluid pump for pumping a clean oil, an electric motor, or an internal combustion engine.
 18. The method of claim 17, wherein: the one or more plunger assemblies comprises two or more plunger assemblies; each plunger assembly comprises an elongated tubular housing and a piston residing within the tubular housing; and each of the respective elongated tubular housings has a first end connected to the sand hopper and a second end connected to the sand manifold.
 19. The method of claim 18, wherein: the elongated tubular housing further comprises an opening along an upper side configured to receive the volume of proppant; and each of the respective pistons comprises a front body and a rear body, with a trough residing between the front body and the rear body, and wherein each of the respective pistons cycles between a retracted position and an extended position such that: when the piston is in its retracted position the trough is aligned with the opening along the corresponding elongated tubular housing to receive a volume of proppant, and when the piston is in its extended position, the trough delivers the volume of proppant into the sand manifold.
 20. The method of claim 18, wherein: the proppant comprises sand; the elongated tubular housing of each of the one or more plunger assemblies is connected to the sand manifold via a housing manifold; and the sand manifold comprises an inlet end for receiving the hydraulic fracturing fluid upstream of the pistons, and an outlet end for delivering the frac slurry comprising the hydraulic fracturing fluid and the proppant.
 21. The method of claim 20, wherein: the prime mover reciprocates the rod and connected piston at a frequency selected to provide a desired concentration of the sand in the frac slurry; the proppant is moved into the sand manifold at a generally constant rate; and the method further comprises determining a concentration of sand for the frac slurry.
 22. The method of claim 20, wherein each of the respective pistons further comprises: a rod that reciprocates linearly along the elongated tubular housing in response to motive power provided by the prime mover; a first end residing at the sand hopper that slidingly receives the rod; a stationary plate residing proximate the first end with the stationary plate having an opening for receiving the rod and serving as a stop member for the rear body when the plunger moves to its retracted position; and a second end residing at a distal end of the front body.
 23. The method of claim 22, wherein each of the one or more respective plunger assemblies further comprises: an elastomeric dart residing at the distal end of the front body but within the sand manifold, serving as a seal to the elongated tubular housing when the plunger moves to its retracted position; a first O-ring residing around an outer diameter of the front body; and a second O-ring residing around an outer diameter of the rear body; wherein the first O-ring and the second O-ring provide a fluid seal for the trough when the plunger moves to its retracted position.
 24. The method of claim 20, wherein each of the one or more respective pistons further comprises: a rod that reciprocates linearly along the elongated tubular housing in response to motive power provided by the prime mover; and a push plate connecting the rod to the first end of the rear body; and wherein: the rear body is connected to the rod, such that the rear body cycles within the elongated tubular housing between retracted and extended positions in response to reciprocation of the rod; and in its retracted position the rear body resides between the base of the sand hopper and the opening along the upper side of the elongated tubular housing.
 25. The method of claim 24, wherein each of the respective plunger assemblies further comprises a one-way valve residing proximate the second end of the elongated tubular housing, wherein the one-way valve extends into the sand manifold.
 26. The method of claim 25, wherein: the front body of each of the respective pistons is stationary and resides at the distal end of its respective elongated tubular housing; and the one-way valve resides at the distal of and is connected to the front body of the one or more respective pistons.
 27. The method of claim 20, further comprising: adjusting a rate of cycling of the pistons.
 28. The method of claim 20, wherein the frac slurry is exposed to no frac iron at the well site until it reaches the frac tree.
 29. A method of forming a hydraulic fracturing slurry, comprising: receiving a plurality of sand boxes at a well site, wherein each of the plurality of sand boxes contains proppant; receiving water and chemicals for a wellbore fracturing operation at the well site; mixing the water and chemicals in selected portions in a blender to form an aqueous frac medium; moving the blended aqueous frac medium through one or more high-pressure pumps; releasing the pressurized and blended aqueous frac medium from the one or more high-pressure pumps into a high-pressure frac line; pumping the blended aqueous frac medium from the high-pressure frac line through a sand manifold; transferring proppant from the sand boxes into the sand manifold in pulses while pumping the blended aqueous frac medium, forming a frac slurry; releasing the frac slurry from the sand manifold back into the high-pressure frac line; and passing the frac slurry from the high-pressure frac line through a frac tree and into the wellbore.
 30. The method of claim 29, wherein: the proppant comprises sand; the proppant is moved into the sand manifold at a generally constant rate; and the frac slurry is pumped into the wellbore at a pressure that is greater than a formation parting pressure of a downhole formation. 